Pseudotetrahedral manganese complexes supported by the anionic tris(phosphino)borate ligand [PhBPiPr3]

Article abstract of DOI:10.1021/ic060735q

This paper presents aspects of the coordination chemistry of mono- and divalent manganese complexes supported by the anionic tris(phosphino)borate ligand, [PhBP^iPr₃] (where [PhBP^iPr₃] = [PhB(CH₂PⁱPr₂)₃]^-). The Mn(II) halide complexes, [PhBP^iPr₃]MnCl (1) and [PhBP^iPr₃]Mnl (2), have been characterized by X-ray diffraction, SQUID magnetometry, and EPR spectroscopy. Compound 2 serves as a precursor to a series of Mn azide, alkyl, and amide species: [PhBP ^iPr₃]Mn(N₃) (3), [PhBP^iPr ₃]Mn(CH₂Ph) (4), [PhBP^iPr₃]Mn(Me) (5), [PhBP^iPr₃]Mn(NH(2,6-ⁱPr₂-C ₆H₃)) (6), [PhBP^iPr₃]Mn(dbabh) (7), and [PhBP^iPr₃]Mn(1-Ph(isoindolate)) (8). The complexes 2-8 feature a divalent-metal center and are pseudotetrahedral. They collectively represent an uncommon structural motif for low-coordinate, polyphosphine- supported Mn complexes. Two Mn(I) species have also been prepared. These include the Tl-Mn adduct [PhBP^iPr₃]Tl-MnBr(CO)₄ (9) and the octahedral complex [PhBP^iPr₃]Mn(CN ^tBu)₃ (10). Some of our initial synthetic efforts to generate [PhBP^iPr₃]Mn=N_x species are briefly described, as are DFT studies that probe the electronic viability of these types of multiply bonded target structures.

Full text of DOI:10.1021/ic060735q

Inorg. Chem. 2006, 45, 8597−8607
Pseudotetrahedral Manganese Complexes Supported by the Anionic
Tris(phosphino)borate Ligand [PhBPiPr
]
3
Connie C. Lu and Jonas C. Peters*
Contribution from the DiVision of Chemistry and Chemical Engineering, Arnold and Mabel
Beckman Laboratories of Chemical Synthesis, California Institute of Technology,
Pasadena, California 91125
Received April 29, 2006
This paper presents aspects of the coordination chemistry of mono- and divalent manganese complexes supported
by the anionic tris(phosphino)borate ligand, [PhBPiPr3] (where [PhBPiPr [PhB(CH2PiPr2)3]-). The Mn(II) halide
]
3
)
complexes, [PhBPiPr3]MnCl (1) and [PhBPiPr3]MnI (2), have been characterized by X-ray diffraction, SQUID
magnetometry, and EPR spectroscopy. Compound 2 serves as a precursor to a series of Mn azide, alkyl, and
amide species: [PhBPiPr3]Mn(N3) (3), [PhBPiPr3]Mn(CH2Ph) (4), [PhBPiPr3]Mn(Me) (5), [PhBPiPr3]Mn(NH(2,6-iPr2-
C6H3)) (6), [PhBPiPr3]Mn(dbabh) (7), and [PhBPiPr3]Mn(1-Ph(isoindolate)) (8). The complexes 2
metal center and are pseudotetrahedral. They collectively represent an uncommon structural motif for low-coordinate,
polyphosphine-supported Mn complexes. Two Mn(I) species have also been prepared. These include the Tl Mn
adduct [PhBPiPr3]Tl MnBr(CO)4 (9) and the octahedral complex [PhBPiPr3]Mn(CNtBu)3 (10). Some of our initial synthetic
efforts to generate [PhBPiPr3]Mn
Nx species are briefly described, as are DFT studies that probe the electronic
viability of these types of multiply bonded target structures.
−8 feature a divalent-
−
−
t
I. Introduction
tion.10,18 Besides having broad synthetic utility, metal-to-
ligand multiply bonded species also serve as biomimetic
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to-ligand multiple bonds were rare for the later metals,23-25
especially for those in the first-row.26 While the paucity of
these compounds was typically attributed to an inherent
Transition metal complexes containing metal-ligand
multiple bonds figure prominently in coordination chemistry,
especially in atom- and group-transfer processes.1,2 Metal
species of the types LnMdE and LnMtE, where E ) O,
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* To whom correspondence should be addressed. E-Mail: jpeters@
caltech.edu.
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10.1021/ic060735q CCC: $33.50
Published on Web 09/22/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 21, 2006 8597

Lu and Peters
incompatibility of high d-electron counts with multiply
bonded π-donor substituents,1 low-coordinate geometries
have provided one strategic path to circumvent this limitation.
The recent rise in literature reports of well-defined LnMdE
and LnMtE systems for the metals M ) Fe,27-33 Co,34-38
Ni,39-43 and Cu44,45 strongly attests to the viability of these
types of species for the first-row, mid-to-late metals.
nitride, [Mn(N)(NtBu)3]2-, which is supported by imido
ligands.59 Other relevant manganese imides from the Hurst-
house group include species of the type MnVII(NtBu)3X, as
well as the homoleptic compound [MnVI(NtBu)4]2-.60-62
Terminal Mn(V) imides are also stabilized by corroles, as
recently reported by Abu-Omar and co-workers.63-65 Finally,
elegant work from Groves and Carreira strongly implicates
Mn(V) acylimides (generated in situ from the nitrides) as
effective group-transfer catalysts to olefin and enol ether
substrates.47,55,66
Manganese compounds featuring multiply bonded terminal
functionalities such as nitrides and imides are far more
abundant than their later first-row counterparts.46 For ex-
ample, Mn(V) nitrides are well known to be stabilized by
various ligand auxiliaries, including porphyrins,47-51 mac-
rocyclic amines,52,53 cyanides,54 and Schiff bases.55-58 In
contrast, Mn(VI) and Mn(VII) nitrides are rare. Wieghardt
and co-workers generated two examples of Mn(VI) nitrides
in situ and assigned them from spectral data.52,54 Hursthouse
and co-workers isolated the sole example of a Mn(VII)
Our group has been investigating the tris(phosphino)borate
(generally denoted as [BP3]) and hybrid bis(phosphino)-
pyrazolylborate ([BP2(pz)]) ligands as scaffolds for MtE
linkages. Our endeavors have led to the characterization of
stable Co(III)36 and Fe(II/III) imides,27,29 as well as distinctive
examples of Fe(IV) imides and nitrides.28,67 Motivated by
these results, we wish to extend this chemistry to other mid-
to-late first-row metals such as Ni68 and Mn. In particular,
we are interested in whether [BP3]MntNx species (d3 and
d4) are electronically accessible and in defining synthetic
methods for their generation. In pursuit of this task, we began
to study aspects of the fundamental coordination chemistry
of previously unexplored [BP3]Mn systems. In this first study,
we report on the synthesis and characterization of a family
of monovalent- and divalent-manganese compounds sup-
ported by the [PhBPiPr3] ligand (where [PhBPiPr3] )
[PhB(CH2PiPr2)3]-), some of which might ultimately serve
as precursors for the preparation of [BP3]MntNx species.
Complementary theoretical studies are described for hypo-
thetical imide [PhBPiPr3]Mn(NtBu) and nitride [PhBPiPr3]Mn-
(N) systems. These species appear to be plausible target
structures on the basis of electronic considerations. While
studies toward well-defined [BP3]MntNx systems are ongo-
ing, the four-coordinate [PhBPiPr3]Mn(II) species that are
described here represent structurally unusual examples of
low-coordinate manganese complexes supported by poly-
phosphine ligands.
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II. Results and Discussion
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Synthesis and Characterization of [PhBPiPr3]Mn(II)
Halides. The Mn(II) halides [PhBPiPr3]MnCl (1) and [PhBPiPr3]-
MnI (2) were readily prepared by mixing the thallium reagent
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8598 Inorganic Chemistry, Vol. 45, No. 21, 2006

Pseudotetrahedral Manganese Complexes Supported by [PhBPiPr
]
3
Figure 1. Displacement ellipsoid representations (50%) of (A) [PhBPiPr3]-
MnCl (1a) and (B) [PhBPiPr3]MnI (2). Hydrogen atoms and solvent mole-
cules have been omitted for clarity. Selected bond distances (Å) and angles
(deg) for 1a: Mn-Cl 2.2687(7), Mn-P1 2.5300(6), Cl-Mn-P1 125.38(2),
Mn-P2 2.5298(6), Mn-P3 2.5289(6), Cl-Mn-P2 120.22(2), Cl-Mn-
P3 126.14(2), P1-Mn-P2 90.55(2), P2-Mn-P3 92.64(2), P1-Mn-P3
92.22(2). For 2: Mn-I 2.6394(4), Mn-P1 2.5351(7), Mn-P2 2.5238(7),
Mn-P3 2.5379(6), P1-Mn-I 127.19(2), P2-Mn-I 122.27(2), P3-Mn-I
124.09(2), P1-Mn-P2 91.39(2), P2-Mn-P3 90.68(2), P1-Mn-P3
90.95(2).
Figure 2. Displacement ellipsoid representations (50%) of {[PhBPiPr3]-
Mn(µ-Cl)}2 (1b) (top). Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg) for 1b: Mn-ClA 2.4625(9),
Mn-ClA 2.5327(9), Mn-ClB 2.4630(9), Mn-ClB 2.525(1), Mn-P1
2.6162(7), Mn-P2 2.6132(7), Mn-P3A 2.552(4), Mn-P3B 2.580(4), P1-
Mn-P2 86.38(2), P3A-Mn-P1 87.13(7), P3B-Mn-P1 94.03(7), P3A-
Mn-P2 92.55(8), P3B-Mn-P2 86.26(7). View of the core of 1b showing
both positions of the disordered chloride and P3 atom (below). The angle
between the Mn2(ClA)2 and Mn2(ClB)2 planes is 41°.
Scheme 1
significantly longer than M-P distances of tris(phosphino)-
borate complexes of later first-row transition metal ions. For
instance, the series of structurally characterized chloride
complexes, [PhBPiPr3]MCl for M ) Mn, Fe, Co, and Ni,
show decreasing M-P bond distances, which reflect both
their decreasing ionic radii across the series as well as their
total spin, S.
The dimer 1b crystallizes in the triclinic crystal system
P1h and features a Mn2Cl2 core that contains an inversion
center. The chloride and one PiPr2 unit are disordered, but
both can be independently refined in two positions of nearly
equal populations. The solid-state structure of one conformer
is shown in Figure 2 (top). A simplified structure containing
all of the disordered atoms in the core is shown below it. In
the dimer, the Mn center is five-coordinate and roughly
square pyramidal. Two phosphorus atoms and two chlorides
comprise the base, with an axial phosphine at the apex of
the pyramid. The Mn-P bond distances in the dimer are
even more elongated relative to the monomer 1a (Mn-P )
2.613, 2.616, and 2.552 Å). One of these bonds (Mn-P3) is
slightly shorter than the other two and corresponds to the
Mn-Pax bond. The Mn-Cl bonds in the dimer are also
significantly longer (2.463 and 2.533 Å) compared to the
monomer (2.269 Å).
Magnetic susceptibility (SQUID) data were obtained on
polycrystalline samples of 1 and 2. The µeff versus T plots
are nearly identical and show very little temperature depen-
dence (Figure 3A). From 60 to 300 K, the µeff values average
5.94 µB for 1 (calculated as a monomer) and 5.97 µB for 2.
The µeff value for 1 is identical to its solution magnetic
moment of 5.9(1) in benzene, where we presume the
monomeric form is favored over the dimer form (Evans
method, three runs).73,74 These values are consistent with five
unpaired electrons per Mn, verifying the high-spin config-
uration of these [PhBPiPr3]MnX species. The proximity of
[PhBPiPr3]Tl with MnX2 (where X ) Cl or I) (Scheme 1).69
This methodology has been used previously by us to prepare
related compounds of divalent Fe, Ru, Co, and Ni.68,70,71 The
halides 1 and 2 are colorless in solution and can be
crystallized from benzene/petroleum ether. Compound 1
provided light pink blocks in low yield (33%), while 2 was
obtained as colorless blocks in moderate yield (62%).
Because of its higher crystalline yield, compound 2 was used
as the preferred starting material throughout the research
described herein.
The halides 1 and 2 were characterized by various
techniques including X-ray crystallography, SQUID mag-
netometry, and EPR spectroscopy. The solid-state structures
of 1 and 2 are shown in Figures 1 and 2. The chloride
complex 1 crystallizes as a mixture of its monomer (1a) and
its dimer {[PhBPiPr3]Mn(µ-Cl)}2 (1b), whereas the iodide
complex 2 crystallizes exclusively as a monomer. A similar
monomer-dimer equilibrium was observed for [PhBP3]CoX
systems in solution (where X ) Cl or Br).71 Solid-state
structures of monomeric 1a and 2 are pseudotetrahedral with
approximate 3-fold symmetry about the axis containing B,
Mn, and X (I-Mn-B ) 176.6°, Cl-Mn-B ) 175.5°). The
Mn-P bond distances are nearly equal, as well as the
P-Mn-P bond angles. For example, monomer 1a has
Mn-P distances of 2.53 Å and P-Mn-P angles that are
near 90° (90.6-92.6°). Likewise, compound 2 exhibits a
narrow spread in its Mn-P bond distances (2.524-2.538
Å) and P-Mn-P angles (90.7-91.4°). The Mn-P bond
distances are not unusual for high-spin Mn(II)72 but are
(69) Shapiro, I. R.; Jenkins, D. M.; Thomas, J. C.; Day, M. W.; Peters, J.
C. Chem. Commun. 2001, 2152.
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Inorganic Chemistry, Vol. 45, No. 21, 2006 8599

Lu and Peters
Figure 3. (A) SQUID plot of µeff (µB) versus T and (B) øMT (cm3K/mol)
versus T for [PhBPiPr3]MnCl, 1, (9), and [PhBPiPr3]MnI, 2, (0). An
expansion of the øMT vs T plot at low temperatures (4-30 K) is shown in
the inset.
Figure 4. EPR spectra of glassy methyl-THF solutions of (A) [PhBPiPr3]-
MnI (2) and (B) [PhBPiPr3]MnCl (1) at 8 K. Instrumental parameters: ν )
9.38 GHz, modulation frequency ) 100 kHz, modulation amplitude ) 5
G, microwave power ) 0.064 mW, conversion time ) 81.9 ms, time
constant ) 20.5 ms, sweep time ) 83.9 ms, 3 scans.
µ
eff to the spin-only value (5.92 µB) further suggests that the
attributed to a superposition of the monomer (∼130 and 360
mT) and dimer forms of 1. The dimer, an S ) 5 paramagnet,
could itself give rise to multiple transitions. For both 1 and
2, hyperfine coupling to the 31P nucleus (I ) 1/2) is not
observed, suggesting that the spin density is tightly localized
on Mn and therefore indicative of attenuated covalent
character at the Mn-P bond by comparison to other [BP3]M
paramagnets we have studied.27,71,78
ground states of 1 and 2 are orbitally nondegenerate as
expected for a ground-state electronic configuration where
all the d orbitals are singly populated (6S). The øMT versus
T plots for 1 and 2 are also similar, but distinct at very low
temperatures. From 4 to 75 K, øMT dips slightly for 2,
perhaps due to intermolecular paramagnetic quenching
(Figure 3B).75 The øMT versus T plot for 1, however, shows
a gradual increase in øMT in the same temperature range.
The small rise in øMT from 4.43 to 4.71 cm3 K/mol might
be indicative of weak ferromagnetic coupling. Similarly weak
coupling has been observed in another Mn(µ-Cl) dimer and
might thus arise from the presence of the dimer 1b.76
EPR spectra were also recorded on the halides in methyl-
THF glass at 8 K. The iodide 2 has an axial spectrum with
transitions at ∼120 and 330 mT (Figure 4A). The observed
g values, ∼ 6 and 2, match the calculated transitions for the
ms ) (1/2 states of a S ) 5/2 paramagnet with E/D ≈ 0.
Hyperfine structure due to the 55Mn nucleus (I ) 5/2) is
evident in the g ) 2 signal, which shows a six-line splitting
with A ≈ 63 G. The octahedral complexes MnX2(dmpe)2
(where X ) Br, I) show nearly identical EPR signatures.77
Unlike 2, the chloride 1 has an EPR spectrum with numerous
transitions occurring from 0 to 1000 mT (Figure 4B). The
complicated spectrum is difficult to interpret and is tentatively
Compounds 1 and 2 were also studied by NMR spectros-
copy and electrochemistry, but these data proved relatively
1
uninformative. The H NMR spectra contained few resolv-
able resonances, and those that could be resolved were unus-
ually broad by comparison to related [PhBPiPr3]FeX and
[PhBPiPr3]CoX systems. The cyclic voltammograms of 1 and
2 did not reveal any reversible features (0.35 M [nBu4N]-
[PF6] in THF). The lack of any reversible redox couples also
contrasts the analogous halide complexes of Fe, Co, and Ni,
all of which exhibit at least pseudoreversible MII/MI redox
couples.
Surprisingly, a survey of the CCDC revealed only three
structures of monomeric four-coordinate Mn halide com-
plexes with one or two phosphine donor(s).72,79,80 No such
structures with three phosphine donors were found. Even
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Dalton Trans. 1993, 371.
8600 Inorganic Chemistry, Vol. 45, No. 21, 2006

Pseudotetrahedral Manganese Complexes Supported by [PhBPiPr
]
3
Scheme 3
Figure 5. Displacement ellipsoid representations (50%) of [PhBPiPr3]Mn-
(N3) (3) and [PhBPiPr3]Mn(CH2Ph) (4). For clarity, hydrogen atoms have
been omitted and only the phosphorus atoms of the ligand are shown. For
3, only one of the two molecules in the asymmetric unit is shown. Selected
bond distances (Å) and angles (deg) for 3: Mn-N1 2.046(3), Mn-P1 2.534-
(1), Mn-P2 2.522(1), Mn-P3 2.521(2), N1-N2 1.112(5), N2-N3 1.202-
(6), N2-N1-Mn 128.8(3), P1-Mn-P2 92.33(4), P2-Mn-P3 93.21(5),
P1-Mn-P3 91.04(5), N1-Mn-P1 123.1(1), N1-Mn-P2 125.7(1), N1-
Mn-P3 122.2(1). For 4: Mn-C28 2.138(2), Mn-P1 2.5679(4), Mn-P2
2.5507(5), Mn-P3 2.5620(5), P1-Mn-P2 91.46(1), P2-Mn-P3 89.44-
(1), P1-Mn-P3 89.90(1), C28-Mn-P1 117.86(5), C28-Mn-P2 126.42-
(5), C28-Mn-P3 130.59(5), Mn-C28-C29 111.5(1).
halides 1 and 2. In a CCDC search of all structurally
characterized Mn complexes containing a terminal azide, the
mean Mn-N bond distance is 2.190 Å with a standard
deviation of 0.096 Å. The Mn-N bond distance of 2.046(3)
Å in 3 is therefore unusually short. Manganese complexes
featuring similarly short Mn-N bond distances for terminal
azides are typically in the oxidation state +3.53,89-92
Scheme 2
Manganese alkyl compounds were also readily prepared
from the addition of alkyl Gringards PhCH2MgBr and
MeMgBr to 2 at -90° in THF. The bright yellow complex
[PhBPiPr3]Mn(CH2Ph) (4) and pale yellow complex [PhBPiPr3]-
Mn(Me) (5) are soluble in hydrocarbons and can be crystal-
lized from cyclopentane at -30 °C. The benzyl complex 4
was characterized by X-ray diffraction, and its solid-state
structure is shown in Figure 5. Related examples of low-
coordinate monomeric organomanganese compounds are
known and include trigonal (â-diketiminato)MnR and tet-
rahedral (P2)MnR2 species, where P2 represents bidentate
phosphine or two PR3 ligands.93-95 Despite the low valence
electron count of these Mn systems, rather little has been
reported concerning their reactivity patterns. One interesting
exception concerns tetrahedral Mn(II) dialkyl compounds
supported by diimine ligands that readily undergo alkyl
migration to the diimine ligand at ambient temperatures.96
We have found that the [PhBPiPr3]-supported manganese
alkyls 4 and 5 are thermally stable up to 65 °C even under
an atmosphere of dihydrogen or CO. This sharply contrasts
the related iron(II) alkyls [PhBPiPr3]Fe-R, which lose alkane
upon exposure to H2 and bind CO readily.97
monomeric five-coordinate polyphosphine-ligated Mn halides
are few in number, with only three structurally characterized
examples.81-83 Low-coordinate Mn halides are also known
for the related tridentate ligand tris(pyrazoyl)borate (Tp). A
handful of monomeric four-coordinate manganese structures
featuring these ligands have been reported.84-88
Synthesis and Characterization of [PhBPiPr3]Mn(II)
Azide, Alkyls, and Amides. A series of divalent-manganese
complexes featuring other X-type ligands were readily
prepared from the iodide 2 via metathesis (Scheme 2). For
example, addition of excess sodium azide to 2 produced off-
white [PhBPiPr3]Mn(N3) (3) in good yield (73%). Compound
3 features a terminal azide ligand with a characteristic ν-
(N3) stretch at 2070 cm-1 (KBr, THF). Its solid-state structure
is shown in Figure 5. Not surprisingly, the pseudohalide 3
exhibits a similar molecular geometry to the monomeric
Manganese amides were generated by the addition of
lithium and potassium amides to 2 at -90° in THF (Scheme
3). In the metathesis reactions with lithium amides, a
(81) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Orlandini, A. J. Chem.
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1987, 126, 39.
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Chem. 2001, 40, 435.
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Soc., Chem. Commun. 1984, 658.
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Moro-oka, Y. J. Am. Chem. Soc. 1915, 37, 6554.
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Inorg. Chem. 2005, 44, 325.
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N.; Duboc-Toia, C. J. Am. Chem. Soc. 2003, 125, 12337.
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S.; Mukherjee, M.; Okamoto, K. I. Polyhedron 2004, 23, 1811.
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Organometallics 2004, 23, 1177.
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Fujisawa, K. Organometallics 2004, 23, 4335.
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Inorg. Chem. 2001, 40, 3170.
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Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1983, 2631.
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Noltemeyer, M. Organometallics 2004, 23, 3284.
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Ebina, F.; Hikichi, S.; Akita, M.; Moro-oka, Y. J. Chem. Soc., Dalton
Trans. 1998, 511.
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(97) Daida, E. J.; Peters, J. C. Inorg. Chem. 2004, 43, 7474.
Inorganic Chemistry, Vol. 45, No. 21, 2006 8601

Lu and Peters
Figure 6. Displacement ellipsoid representations (50%) of [PhBPiPr3]Mn(NH(2,6-iPr2-C6H3)) (6), [PhBPiPr3]Mn(dbabh) (7), and [PhBPiPr3]Mn(1-Ph(isoindolate))
(8). For clarity, hydrogen atoms (except N-H) have been omitted and only the phosphorus atoms of the ligand are shown. Selected bond distances (Å) and
angles (deg) for 6: Mn-N 1.997(2), Mn-P1 2.5877(6), Mn-P2 2.5813(6), Mn-P3 2.5637(6), P1-Mn-P2 87.96(2), P2-Mn-P3 89.95(2), P1-Mn-P3
93.11(2), N-Mn-P1 144.77(5), N-Mn-P2 105.73(5), N-Mn-P3 118.63(5). For 7: Mn-N 1.948(1), Mn-P1 2.5357(5), Mn-P2 2.5473(5), Mn-P3
2.5503(5), P1-Mn-P2 90.46(2), P2-Mn-P3 89.51(2), P1-Mn-P3 90.71(2), N-Mn-P1 126.19(4), N-Mn-P2 126.13(4), N-Mn-P3 122.92(4). For 8:
Mn-N 2.054(2), Mn-P1 2.5308(7), Mn-P2 2.5550(7), Mn-P3 2.5718(6), P1-Mn-P2 95.13(2), P1-Mn-P3 89.54(2), P2-Mn-P3 90.09(2), N-Mn-
P1 111.98(5), N-Mn-P2 136.31(5), N-Mn-P3 122.30(5).
common side-product was the free ligand [PhBPiPr3][Li],
easily identified by 31P NMR spectroscopy. Replacement of
lithium by potassium minimizes the liberation of the [PhB-
PiPr3] anion. For example, 2,6-diispropylaniline can be
deprotonated with KH and added to 2 to produce yellow
[PhBPiPr3]Mn(NH(2,6-iPr2-C6H3)) (6) in high yield (90%).
This strategy was also employed to install 2,3:5,6-dibenzo-
7-azabicyclo[2.2.1]hepta-2,5-diene (Hdbabh) as the amide
Figure 7. Cyclic voltammagram of [PhBPiPr3]Mn(dbabh) (7) recorded at
a scan rate of 50 mV/s in THF with 0.35 M [nBu4][PF6] as the supporting
functionality. The lithium amide Li(dbabh) is a particularly
interesting reagent to investigate because it has been suc-
cessfully exploited as an N-atom transfer reagent to both Cr
and Fe centers with concomitant loss of anthracene.28,98
Methathesis of 2 and Li(dbabh) resulted in a mixture of the
amide compound [PhBPiPr3]Mn(dbabh) (7), the bridged amide
complex {(Hdbabh)MnI(µ-N-dbabh)}2 (see Supporting In-
formation), and the ligand [PhBPiPr3][Li]. Though the yield
of the desired compound 7 was quite low, yellow crystals
of 7 could be cleanly chosen from the colorless crystals of
the byproducts. Attempts to improve the yield of 7 by using
K(dbabh) were unsuccessful. Deprotonation of Hdbabh with
KH or benzyl potassium afforded a bright yellow-green
solution; upon addition of 2 at -90 °C, the reaction solution
turned orange. Red-orange crystals were grown from this
solution that were clearly indicative of a species different
from 7. An X-ray diffraction study revealed the product to
be a different Mn amide, [PhBPiPr3]Mn(1-Ph(isoindolate))
(8), an isomer of 7 wherein one of the five-membered rings
has opened by an overall C-C bond cleavage. This
decomposition most likely occurs during the deprotonation
stage of the reaction since the solution turns brilliant yellow-
green upon addition of the potassium base, whereas solutions
of Li(dbabh) are pale pink.
electrolyte. Potentials are internally referenced to Fc/Fc+.
90°). The apical N atom of 7 lies on the Mn-B axis, whereas
compounds 6 and 8 exhibit a slightly canted N atom with
N-Mn-B angles of 156° and 167°, respectively. The Mn-N
bond distances follow the order: 7 (1.948(1) Å) < 6 (1.997-
(2) Å) < 8 (2.054(2) Å). This trend likely reflects the relative
steric repulsion between the amide groups and the isopropyl
groups of the [PhBPiPr3] ligand.
The Mn(II) alkyls and amides were studied by cyclic
voltammetry in THF with 0.35 M [nBu4N][PF6] as the
supporting electrolyte and Ag/AgNO3 as the reference
electrode. Interestingly, amide 7 is distinct among this series
of complexes in that it exhibits a reversible one-electron
redox couple centered at -0.26 V (vs Fc/Fc+, scan rate )
50 mV/s), indicative of a MnII/MnIII redox event (Figure 7).
The amides 6 and 8 exhibit irreversible oxidative events near
this same potential.
Synthesis and Characterization of [PhBPiPr3]Mn(I)
Compounds. Monovalent-manganese compounds may prove
to be valuable precursors to MntNR multiply bonded
species in future studies. Indeed, oxidative nitrene transfer
to Fe(I) and Co(I) precursors has proven highly effective in
the synthesis of related FetNR, CotNR, and CodNR
species.29,34-36,99,100 While monovalent-manganese complexes
are numerous, they typically are octahedral 18-electron
species stabilized by carbonyl ligands.101-105 Low-coordinate
and unsaturated Mn(I) compounds, on the other hand, are
uncommon. Notable examples of this latter class include a
The solid-state structures of the Mn(II) amides 6, 7, and
8 are shown in Figure 6. Collectively, these amides are
similar to the other pseudotetrahedral, high-spin [PhBPiPr3]-
Mn(II) species reported here in that they have typical Mn-P
bond distances (ca. 2.55 Å) and P-Mn-P bond angles (ca.
(98) Mindiola, D. J.; Cummins, C. C. Angew. Chem., Int. Ed. 1998, 37,
(99) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 10782.
(100) Hu, X.; Meyer, K. J. Am. Chem. Soc. 2004, 126, 16322.
945.
8602 Inorganic Chemistry, Vol. 45, No. 21, 2006

Pseudotetrahedral Manganese Complexes Supported by [PhBPiPr
]
3
Figure 9. Displacement ellipsoid representations (50%) of [PhBPiPr3]Mn-
(CNtBu)3 (10) from the side (A) and top (B) views. For clarity, hydrogen
atoms have been omitted and only the phosphorus atoms of the ligand are
shown. Selected bond distances (Å) and angles (deg) for 10: Mn-C28
1.870(1), Mn-C33 1.864(1), Mn-C38 1.835(1), N1-C28 1.176(2), N2-
C33 1.176(2), N3-C38 1.185(2), Mn-P1 2.3597(4), Mn-P2 2.3831(4),
Mn-P3 2.3655(3), P1-Mn-P2 88.59(1), P2-Mn-P3 86.49(1), P1-Mn-
P3 89.17(1), C33-Mn-C28 83.75(5), C38-Mn-C28 85.26(5), C38-Mn-
C33 89.12(5).
Figure 8. Displacement ellipsoid representations (50%) of [PhBPiPr3]Tl-
MnBr(CO)4 (9). For clarity, hydrogen atoms have been omitted. Selected
bond distances (Å) and angles (deg) for 9: Mn-Tl 2.6437(4), Mn-C28
1.913(3), Mn-C29 1.799(3), Mn-C30 1.851(3), Mn-C31 1.823(3), Mn-
Br 2.5299(4), C31-Mn-Tl 172.74(8), Br-Mn-Tl 86.11(1), C29-Mn-
C28 92.6(1), C29-Mn-C30 91.1(1), C28-Mn-Br 85.39(7), C29-Mn-
Br 177.98(8), C30-Mn-Br 90.94(8), C31-Mn-Br 86.73(8).
three-coordinate Mn(I) dimer supported by bulky â-diketimi-
nate ligands and several five-coordinate Mn compounds of
the type (P∧P)2Mn(CO)+ (where P∧P is a bidentate
phosphine).106-109
To pursue a low-coordinate Mn(I) precursor, [PhBPiPr3]-
Tl and MnBr(CO)5 were heated in benzene at 50 °C for
several hours. The resulting yellow solution contained some
TlBr precipitate, but to our surprise, the major product was
a Tl-Mn adduct, [PhBPiPr3]Tl-MnBr(CO)4 (9), which was
isolated in 39% crystalline yield. Compound 9 is diamagnetic
and exhibits a doublet in the 31P NMR spectrum (45.4 ppm,
JTl-P ) 8060 Hz) that is shifted relative to [PhBPiPr3]Tl (24.3
ppm, JTl-P ) 5913 Hz). The solid-state structure of 9 is
shown in Figure 8. There are several crystal structures
featuring a Tl-Mn bond, and the Tl-Mn bond of 2.6437-
(4) Å is similar to those reported previously.110,111
Figure 10. Cyclic voltammagram of [PhBPiPr3]Mn(CNtBu)3 (10) recorded
at a scan rate of 100 mV/s in THF with 0.35 M [nBu4][PF6] as the supporting
electrolyte. Potentials are internally referenced to Fc/Fc+.
Scheme 4
Prolonged heating of a benzene solution of 9 resulted in
its decomposition. By 31P NMR spectroscopy, one major
product forms upon thermolysis, characterized by a broad
peak at ∼50 ppm. An IR spectrum revealed two sharp
stretches at 1999 and 1906 cm-1 (KBr/THF). We propose
this species to be the Mn(I) tricarbonyl compound, [PhBPiPr3]-
Mn(CO)3 (Scheme 4). Indeed, the isoelectronic compound,
[PhBPiPr3]Mn(CNtBu)3 (10), can be prepared by the reduction
of [PhBPiPr3]MnI with sodium naphthalenide followed by
addition of excess CNtBu. Compound 10 is isolated in pure
form but in low yield (22%) due in part to the competitive
formation of [PhBPiPr3]Na.112 Similarly, reduction of [PhBPiPr3]-
MnI with sodium naphthalenide under CO produces the
presumed degradation product of 9, [PhBPiPr3]Mn(CO)3.
Unfortunately, this species has not been isolated in pure form.
The solid-state structure of 10 confirms its assignment as a
monovalent-Mn complex with three isocyanides (Figure 9).
Relative to the high-spin Mn(II) species, the Mn-P bonds
(2.36-2.38 Å) are more than 0.15 Å shorter. The P-Mn-P
bond angles are also slightly contracted (86.5-89.2°).
Compound 10 is also characterized by a reversible redox
process at -0.66 V in its cyclic voltammagram, shown in
Figure 10 (vs Fc/Fc+, scan rate ) 100 mV/s).
(101) Baker, R. J.; Edwards, P. G.; Gracia-Mora, J.; Ingold, F.; Malik, K.
M. A. J. Chem. Soc., Dalton Trans. 2002, 3985.
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(112) Attempts to minimize formation of [PhBPiPr3]Na by adding CNtBu
to 2 prior to the addition of sodium naphthalenide or by adding
sodium naphthalenide to 2 at low temperatures gave rise to more
complex reaction mixtures.
Inorganic Chemistry, Vol. 45, No. 21, 2006 8603

Lu and Peters
Figure 12. DFT-optimized structures (Jaguar 5.0, B3LYP/LACVP**) for
(A) doublet [PhBPiPr3]Mn(N) and (B) quartet [PhBPiPr3]Mn(N). Selected
bond distances (Å) and angles (deg) for (A): Mn-N 1.50; Mn-P 2.35,
2.41, 2.45; N-Mn-P 112.1, 122.3, 127.5; P-Mn-P 94.8, 95.6, 97.2. For
(B): Mn-N 1.62; Mn-P 2.48, 2.49, 2.60; N-Mn-P 103.9, 109.3, 155.3;
P-Mn-P 89.9, 90.5, 91.2.
Figure 11. DFT-optimized structures (Jaguar 5.0, B3LYP/LACVP**) for
(A) singlet [PhBPiPr3]Mn(NtBu) and (B) triplet [PhBPiPr3]Mn(NtBu). Selected
bond distances (Å) and angles (deg) for (A): Mn-N 1.63; Mn-P 2.28,
2.36, 2.36; Mn-N-C 144.8; P-Mn-P 96.8, 97.2, 97.7; N-Mn-P 104.7,
126.2, 127.2. For (B): Mn-N 1.66; Mn-P 2.40, 2.44, 2.45; Mn-N-C
179.2; P-Mn-P 89.5, 89.8, 91.5; N-Mn-P 121.9, 126.2, 127.0.
fact that it is predicted by DFT to be more energetically stable
by 0.74 eV than the singlet state.
DFT Models of MndNtBu and MntN Species. DFT
studies were undertaken to obtain some insight on the
electronic viability of two species, [PhBPiPr3]MnIIItNtBu and
[PhBPiPr3]MnIVtN. We have previously used DFT methods
to probe the electronic structures of [BP3]M species with
terminally bound Nx functionalities that are strongly π-donat-
ing, for example [PhBP3]CoIIItN(p-tolyl), [PhBP3]FeIIIt
NtBu, and [PhBPiPr3]FeIVtN.29,36,28
On the basis of DFT studies, the known nitride [PhBPiPr3]-
FeIVtN has a splitting diagram that differs from the
2
structurally analogous imides in that the a1 orbital of dz
parentage is more appreciably destabilized by σ antibonding
interactions with the nitride functionality and the phosphine
donors.28 This situation leaves only two orbitals at very low
energy, giving rise to the singlet ground state of [PhBPiPr3]-
FeIVtN. On the basis of this splitting scheme, the hypotheti-
cal Mn nitride [PhBPiPr3]MntN might be expected to
populate a doublet ground state. To ascertain whether this
would be the case, the Mn nitride [PhBPiPr3]Mn(N) was
modeled as both an S ) 1/2 and 3/2 system. In the optimized
quartet structure, the nitride atom is severely tilted off the
Mn-B axis by 30° (Figure 12B) in what appears to be an
unfavorable geometry. The P-Mn-P bond angles (90-91°)
and Mn-P bond distances (2.48-2.60 Å) are, however,
typical of the pseudotetrahedral [PhBPiPr3]Mn(II) complexes
described here. The Mn-N bond length of 1.62 Å seems
excessively long for known MntN species, which typically
have Mn-N bond lengths in the range of 1.50-1.55 Å.
These distortions in the optimized quartet structure presum-
For the low-spin Fe and Co imides, a general d-orbital
splitting diagram has been forwarded based upon these DFT
studies. The d orbitals, which transform as a1 + 2e under
idealized 3-fold symmetry, split into two high-lying and three
lower-lying orbitals. The higher-energy e set, which in
simplest terms can be thought of as comprising dxz and dyz,
is destabilized by σ* and π* interactions with the phosphines
and imide functionality, respectively. The remaining orbitals,
2
2
2
of predominant dz (a1) and dxy and dx -y (e) character, lie at
lower energy and are predominantly nonbonding in nature.27
If we apply this qualitative d-orbital picture to the
hypothetical d4 imide, [PhBPiPr3]MntNtBu, the two ground
states low-spin (S ) 0) and intermediate-spin (S ) 1) need
to be considered. Recently, we have reported the character-
ization of an unusual FeIV imide that exhibits a triplet ground
state.67 Because this species is isoelectronic to the hypotheti-
cal Mn(III) imide under consideration here, we might expect
the latter to be a triplet as well. To test this from a theoretical
standpoint, the imide [PhBPiPr3]MntNtBu was optimized as
a singlet and a triplet using the Jaguar computational program
(B3LYP/LACVP**). The input geometry was derived from
the crystal structure coordinates of [PhBPiPr3]Fe(NAd), where
the metal and Nx functionality were changed to Mn and NtBu,
respectively. A geometry optimization was then performed
using a spin-unrestricted calculation and conducted without
any symmetry constraints (see Supporting Information).
2
ably arise from population of the antibonding dz orbital.
Relative to the quartet state, the doublet state is energeti-
cally preferred by 0.41 eV and exhibits what appears to be
a more reasonable geometry (Figure 12A). The nitride atom
is canted off the Mn-B axis by only 9° and binds tightly to
Mn with a Mn-N bond length of 1.50 Å. The P-Mn-P
bond angles are slightly expanded (95-97°), approaching a
more tetrahedral geometry. Similar parameters were found
in the DFT-optimized structure of [PhBPiPr3]FeIVtN, which
features expanded P-Fe-P bond angles (99-101°) and an
Fe-N bond length of 1.49 Å. It is the combination of these
2
two structural parameters that renders the a1 (dz ) orbital more
antibonding for the metal nitrides than in the case of the
related metal imides.
The predicted structures for the singlet and triplet states
of [PhBPiPr3]MntNtBu differ quite remarkably from one
another (Figure 11). The optimized singlet structure has a
bent Mn-N-C angle (145°) with expanded P-Mn-P
angles (97-98°), whereas the optimized triplet structure
features a linear Mn-N-C angle (179°) with characteristic
P-Mn-P angles (90-92°). The triplet state exhibits what
appears to be a more likely geometry, in accord with the
III. Concluding Remarks
With this report, we have extended our study of the
coordination chemistry of first-row mid-to-late transistion
metals supported by electron-releasing [BP3] ligands. As with
Fe, Co, and Ni, the [PhBPiPr3] scaffold readily supports Mn-
8604 Inorganic Chemistry, Vol. 45, No. 21, 2006

Pseudotetrahedral Manganese Complexes Supported by [PhBPiPr
]
3
heat and ignition sources.) Potassium hydride was crushed into a
fine powder, washed liberally with petroleum ether, and stored at
-30 °C. All other reagents were purchased from commercial
vendors and used without further purification. Elemental analyses
were performed by Desert Analytics, Tucson, AZ. Varian 300 MHz
(II) complexes in a pseudotetrahedral geometry. The prepara-
tive significance of the systems described herein is best
underscored by noting how uncommon low-coordinate
manganese complexes supported by polyphosphines are. The
high donor strength and anionic charge of the [PhBPiPr
]
3
1
spectrometers were used to record the H NMR and 31P NMR
ligand may be advantageous over other polyphosphine
ligands in general by helping to attenuate problematic
phosphine dissociation. These two ligand properties are not
always sufficient, however, as evident from the observed
propensity to substitute manganese by an alkali metal cation
or by thallium in the [PhBPiPr3] binding pocket under certain
metathetical exchange reactions. Fortunately, the halide
[PhBPiPr3]MnI does serve as a sufficiently useful reagent for
most metathetical reactions, allowing the preparation of
[PhBPiPr3]Mn(II) azide, alkyl, and amide species.
DFT calculations of the hypothetical Mn(III) imide
[PhBPiPr3]Mn(NtBu) and Mn(IV) nitride [PhBPiPr3]Mn(N)
structures suggest that their preferred ground states will be
triplet and doublet, respectively. While the preparation of
MntNx species of these types has, at this stage, only been
cursorily canvassed, it is worth noting a few experimental
observations. For instance, we have explored whether the
Mn(I) complex 10 might undergo facile oxidative group
transfer in the presence of organic aryl and alkyl azides. We
have also canvassed conditions that might have effected the
oxidative deprotonation of the anilide species 6.42 Finally,
attempts to generate a Mn(IV) nitride species, including
thermolysis and photolysis of the amide complex 7, as well
as photolysis of the Mn azide 3, have been explored. As
yet, none of these straightforward approaches have provided
a tractable MntNx species. While the preparation of well-
defined low-valent Mn complexes with multiply bonded
linkages remains a challenge, it is one that should be
surmountable. Our hope is that manganese imides and
nitrides of these types will benefit from synthetic access to
unsaturated Mn(I) precursors, such as a four-coordinate
[PhBPiPr3]Mn-PR3 species. Oxidative nitrene or nitride group
transfer might then prove synthetically more fruitful. Efforts
along these lines are part of ongoing studies in our labs.
spectra at ambient temperature. 1H chemical shifts were referenced
to residual solvent, while 31P NMR chemical shifts were referenced
to 85% H3PO4 at 0 ppm. IR measurements were obtained with a
KBr solution cell using a Bio-Rad Excalibur FTS 3000 spectrometer
controlled by Bio-Rad Merlin Software (v. 2.97) set at 4 cm-1
resolution. Electrochemical measurements were recorded in a
glovebox under a dinitrogen atmosphere using a BAS CV 100W
(Bioanalytical Systems, Inc., West Lafayette, IN). A glassy carbon
working electrode, a platinum wire auxiliary-electrode, and an Ag/
AgNO3 nonaqueous reference electrode were used in the electro-
chemical studies. X-ray diffraction studies were carried out in the
Beckman Institute Crystallographic Facility on a Bruker Smart 1000
CCD diffractometer. Crystals were mounted on a glass fiber with
Paratone-N oil.
EPR Measurements. X-band EPR measurements were recorded
using a Bruker EMX spectrometer (controlled by Bruker Win EPR
software version 3.0) equipped with a rectangular cavity working
in the TE102 mode. Low-temperature measurements were conducted
with an Oxford continuous-flow helium cryostat. Accurate fre-
quency values were recorded from a frequency counter on the
microwave bridge. Solution spectra were acquired in 1-methyltet-
rahydrofuran. Samples were prepared in a glovebox under dinitro-
gen in quartz EPR tubes equipped with ground-glass joints.
Magnetic Measurements. Magnetic measurements were re-
corded using a Quantum Designs SQUID magnetometer running
Magnetic Property Measurement System Rev. 2 software. Data were
recorded at 5000 G. The sample was suspended in the magnetometer
in a plastic straw sealed under nitrogen with Lilly No. 4 gel caps.
Loaded samples were centered within the magnetometer using the
DC centering scan at 35 K and 5000 G. Data were acquired at
4-30 K (one data point every 2 K) and 30-300 K (one data point
every 5 K). The magnetic susceptibility was adjusted for diamag-
netic contributions using the constitutive corrections of Pascal’s
constants. The molar magnetic susceptibility (øm) was calculated
by converting the calculated magnetic susceptibility (ø) obtained
from the magnetometer to a molar susceptibility (using the
multiplication factor {(molecular weight)/[(sample weight)(field
strength)]}). Effective magnetic moments were calculated using the
equation below
Experimental Section
All manipulations were carried out using standard Schlenk or
glovebox techniques under a dinitrogen atmosphere. Unless oth-
erwise noted, solvents were deoxygenated and dried by thorough
sparging with N2 gas followed by passage through an activated
alumina column. Nonhalogenated solvents were tested with a
standard purple solution of benzophenone ketyl in tetrahydrofuran
to confirm effective oxygen and moisture removal. Deuterated
solvents were purchased from Cambridge Isotopes Laboratories,
Inc. and were degassed and stored over activated 3-Å molecular
sieves prior to use. The compounds [PhBPiPr3]Tl,70 benzyl potas-
sium,113 and Li(dbabh)98 were prepared according to literature
µeff ) (7.997ømT)1/2
Computational Methods. All calculations were performed using
the Jaguar 5.0 program package (Jaguar 5.0, Schrodinger, LLC,
Portland, OR). The calculation employed the hybrid DFT functional
B3LYP and the basis set LACVP**. Input coordinates for the
geometry optimizations were derived from the solid-state structure
of [PhBPiPr3]FetNAd, where Fe was replaced by Mn.99 For the
Mn imide, the adamantyl group was truncated to a tert-butyl group;
and for the nitride, the adamantyl group was removed completely.
Spin states and molecular charges were imposed as described in
the text. The calculations were spin-unrestricted, and no symmetry
constraints were used. The default values for geometry and SCF
iteraction cutoffs were used, and all structures converged under
these criteria.
t
procedures. The reagents 2,6-diisopropyl aniline and BuNC were
dried over sieves prior to use. Sodium azide was carefully dried
by heating at 50 °C under vacuum for 2 days. (CAUTION: Azides
are potentially explosiVe and should generally be stored away from
(113) Bailey, P. L.; Coxall, R. A.; Dick, C. M.; Fabre, S.; Henderson, L.
C.; Herber, C.; Liddle, S. T.; Lorono-Gonzalez, D.; Parkin, A.;
Parsons, S. Chem. Eur. J. 2003, 9, 4820.
Synthesis of [PhBPiPr3]MnCl (1). A THF solution (18 mL) of
[PhBPiPr3]Tl (250.0 mg, 36.46 mmol) was added dropwise to a
Inorganic Chemistry, Vol. 45, No. 21, 2006 8605

Lu and Peters
Table 1. X-ray Diffraction Experimental Details for Compounds 1a, 1b, 2-4, and 6-10
1a
1b
2
3
4
chemical formula
0.98C27H53BP3MnCl‚
0.02TlC27H53BP3
C54H106B2Cl2Mn2P6
C27H53BP3MnI‚C6H6
0.77C27H53BP3MnN3‚
C34H60BMnP3
0.05TlC27H53BP3‚
0.18C27H53BP3MnCl
fw
573.66
100
1143.61
100
741.36
100
1165.21
100
627.48
100
T (K)
λ (Å)
a (Å)
b (Å)
c (Å)
R (°)
â (°)
0.71073
14.493(2)
12.928(2)
34.850(5)
90
100.344(3)
90
6424(2)
C2/c (No. 15)
8
0.71073
10.950(2)
11.718(2)
13.432(3)
68.000(3)
76.424(4)
78.528(3)
1541.5(5)
P1h (No. 2)
1
0.71073
9.5424(8)
9.9006(8)
19.668(2)
89.780(1)
89.920(1)
82.662(1)
1842.9(3)
P1h (No. 2)
2
0.71073
11.946(2)
34.586(7)
15.423(3)
90
0.71073
9.4120(6)
11.8746(8)
16.736(1)
90
105.605(1)
90
1801.6(2)
P21 (No. 4)
2
90
90
γ (°)
V (Å3)
space group
Z
6372(2)
Pnc2 (No. 30)
4
1.215
8.3
D
calcd (g/cm3)
1.186
7.3
0.0422, 0.0720
1.232
6.9
0.0356, 0.0674
1.336
13.5
0.0305, 0.0586
1.157
5.2
0.0328, 0.0570
µ (cm-1
)
R1, wR2 (I > 2σ(I))a
0.0938, 0.0783
6
7
8
9
10
chemical formula
fw
T (K)
C39H71BMnNP3
712.63
100
C41H63BMnNP3
728.58
100
C41H63BMnNP3‚0.50C4H10O
765.64
98
C31H53BBrMnO4P3Tl
932.67
100
C42H80BMnN3P3
785.75
100
λ (Å)
0.71073
10.690(1)
11.249(1)
18.718(2)
98.393(2)
101.614(2)
107.482(2)
2050.8(4)
P1h (No. 2)
2
0.71073
10.4294(9)
16.812(1)
23.393(2)
90
97.476(1)
90
4066.7(6)
P21/c (No. 14)
4
0.71073
19.6218(9)
77.737(4)
11.2629(6)
90
0.71073
10.2574(5)
18.6613(8)
19.9243(9)
90
100.590(1)
90
3748.9(3)
P21/n (No. 14)
4
0.71073
11.2996(7)
17.578(1)
23.108(1)
90
93.660(2)
90
4580.4(5)
P21/n (No. 14)
4
a (Å)
b (Å)
c (Å)
R (°)
â (°)
90
90
γ (°)
V (Å3)
space group
Z
17180(2)
Fdd2 (No. 43)
16
1.184
4.5
D
calcd (g/cm3)
1.154
4.7
0.0419, 0.0694
1.190
4.7
0.0409, 0.0724
1.652
58.6
0.0355, 0.0532
1.139
4.2
0.0437, 0.0707
µ (cm-1
R1, wR2 (I > 2σ(I))a
)
0.0514, 0.0731
a R1 ) ∑|| Fo| - |Fc||/∑| Fo|, wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
2
2
2
stirring THF suspension of MnCl2 (46.3 mg, 36.36 mmol). The
reaction mixture was stirred for 24 h and filtered through a Celite
pad. The colorless solution was concentrated under reduced pressure
to dryness to yield an off-white solid. After the solid was washed
liberally with petroleum ether, the product was extracted into
benzene. Vapor diffusion of petroleum ether into the benzene
solution resulted in pale pink blocks (80 mg, 33% yield). 1H NMR
(C6D6, 300 MHz) δ ∼20 (v. br), 10.3 (br), 8.1 (br). Anal. Calcd
for C27H53BClMnP3: C 56.71; H 9.34; N 0. Found: C 56.43; H
9.44; N 0.19.
[PhBPiPr3]MnI (2). A THF solution (20 mL) of [PhBPiPr3]Tl
(284.7 mg, 41.52 mmol) was added dropwise to a stirring THF
suspension of MnI2 (129.5 mg, 41.52 mmol). The reaction mixture
was stirred for 12 h and filtered through a Celite pad. The colorless
solution was concentrated under reduced pressure to dryness to yield
an off-white solid. After the solid was washed liberally with
petroleum ether, the product was extracted into hot benzene. Vapor
diffusion of petroleum ether into the benzene solution resulted in
colorless crystals (172 mg, 62% yield). 1H NMR (C6D6, 300 MHz)
δ 21 (v. br), 8.8 (br), 6.6 (br). Anal. Calcd for C27H53BIMnP3: C
48.89; H 8.05; N 0. Found: C 49.12; H 7.54; N < 0.05.
into the benzene solution. 1H NMR (C6D6, 300 MHz) δ 11 (v. br),
8.3 (br). Anal. Calcd for C27H53BMnN3P3: C 56.07; H 9.24; N
7.26. Found: C 55.67; H 8.85; N 7.34.
[PhBPiPr3]Mn(CH2Ph) (4). An Et2O solution of benzylmagne-
sium bromide (107 µL, 1.41 M) was added dropwise to a THF
solution of [PhBPiPr3]MnI (100.0 mg, 0.151 mmol) chilled to -90
°C. The solution was allowed to warm slowly to room temperature.
The yellow solution was filtered through a Celite pad, concentrated
under reduced pressure to dryness, and extracted with petroleum
ether (83.4 mg, 88% yield). Yellow block crystals suitable for X-ray
1
diffraction were grown from cyclopentane at -30 °C. H NMR
(C6D6, 300 MHz) δ 16 (v. br), 10.3 (br), 8.3 (br). Anal. Calcd for
C34H60BMnP3: C 65.08; H 9.64; N 0. Found: C 64.98; H 9.32; N
<0.05.
[PhBPiPr3]Mn(Me) (5). An Et2O solution of methylmagnesium
bromide (53.5 µL, 2.82 M) was added dropwise to a THF solution
of [PhBPiPr3]MnI (100.0 mg, 0.151 mmol) chilled to -90 °C. The
solution was allowed to warm slowly to room temperature. The
pale yellow solution was filtered through a Celite pad, concentrated
under reduced pressure to dryness, and extracted with petroleum
ether (74.1 mg, 89% crude yield). Crystals were grown from
[PhBPiPr3]Mn(N3) (3). A THF solution (15 mL) of [PhBPiPr3]-
MnI (406.0 mg, 0.612 mmol) was added to a THF suspension of
NaN3 (203.0 mg, 3.06 mmol). The reaction mixture was stirred for
12 h and filtered through a Celite pad. The cream-colored filtrate
was concentrated under reduced pressure to dryness and extracted
with benzene (258 mg, 73% yield). Single crystals suitable for X-ray
diffraction were grown from vapor diffusion of petroleum ether
cyclopentane at -30 °C (42.3 mg, 51% yield). H NMR (C6D6,
1
300 MHz) δ ∼17 (v. br), 10.1 (br), 8.3 (br). Anal. Calcd for C28H56-
BMnP3: C 60.99; H 10.24; N 0. Found: C 60.85; H 9.94; N <0.05.
[PhBPiPr3]Mn(NH(2,6-iPr2-C6H3)) (6). A THF solution (8 mL)
of 2,6-diisopropylaniline (25.1 mg, 0.142 mmol) was added
dropwise to a THF suspension of KH (5.7 mg, 0.142 mmol) chilled
to -90 °C. The solution was allowed to warm slowly to room
8606 Inorganic Chemistry, Vol. 45, No. 21, 2006

Pseudotetrahedral Manganese Complexes Supported by [PhBPiPr
]
3
temperature. After being stirred for 12 h, the solution was rechilled
to -90 °C and a THF solution (8 mL) of [PhBPiPr3]MnI (93.9 mg,
0.142 mmol) was added dropwise. After slowly warming to room
temperature, the bright yellow reaction was concentrated under
reduced pressure to dryness. The product can be extracted with
petroleum ether, filtered through a Celite pad to remove salts, and
concentrated under reduced pressure to afford yellow solids (90.9
mg, 90% yield). Single crystals suitable for X-ray diffraction were
Vapor diffusion of petroleum ether into the solution afforded
yellow-orange crystals (79.2 mg, 39% yield). 1H NMR (C6D6, 300
MHz) δ 7.76 (d, J ) 6.9 Hz, 2H, Ho of Ph), 7.53 (t, J ) 6.9 Hz,
2H, Hm of Ph), 7.30 (t, J ) 6.9 Hz, 1H, Hp of Ph), 2.00 (m, 6H,
CH2P), 1.26 (m, 6H, CHMeMe′), 1.09 (d, J ) 6.9 Hz, 18H,
CHMeMe′), 1.01 (d, J ) 6.9 Hz, 18H, CHMeMe′). 31P NMR (C6D6,
121 MHz) δ 45.4 (d, JTl-P ) 8060 Hz). Anal. Calcd for C31H53-
BBrMnO4P3Tl: C 39.92; H 5.73; N 0. Found: C 40.35; H 5.83; N
0.06.
1
grown from TMS2O/petroleum ether at -30 °C. H NMR (C6D6,
300 MHz) δ 16.3 (v. br), 10.7 (br), 8.1 (br). Anal. Calcd for C39H71-
BMnNP3: C 65.73; H 10.04; N 1.97. Found: C 65.81; H 9.71; N
1.88.
[PhBPiPr3]Mn(CNtBu)3 (10). A THF solution (5 mL) of sodium
naphthalenide (0.237 mmol, prepared by stirring excess Na and
stoichiometric naphthalene in THF for 2 h, filter prior to use) was
added to a stirring solution of [PhBPiPr3]MnI (150.0 mg, 0.226
mmol). tButylisocyanide (43.7 µL, 0.724 mmol) was then quickly
added to the mixture. After 11 h, the reaction mixture was
concentrated under reduced pressure to dryness, extracted with Et2O,
and filtered through a glass wool pipet. The solution was again
concentrated under reduced pressure to dryness, extracted with
petroleum ether, and filtered through a glass wool pipet. Cooling
of the solution to -30 °C afforded pale yellow crystals (39.4 mg,
[PhBPiPr3]Mn(dbabh) (7). A THF solution (5 mL) of [PhBPiPr3]-
MnI (142.2 mg, 0.214 mmol) was added dropwise to a Et2O
suspension (10 mL) of Li(dbabh) (42.7 mg, 0.214 mmol) chilled
to -90 °C. The solution was allowed to warm slowly to room
temperature. The yellow solution was filtered through a Celite pad,
concentrated under reduced pressure to dryness, and extracted with
hot Et2O. Cooling the ether solution to -30 °C afforded yellow
blocks (49.7 mg, 32% yield). 1H NMR (C6D6, 300 MHz) δ 21 (v.
br), 10.3 (br), 8.1 (br). Anal. Calcd for C41H63BMnNP3: C 67.59;
H 8.72; N 1.92. Found: C 66.28; H 8.40; N 1.77.
1
22% yield). H NMR (C6D6, 500 MHz) δ 8.15 (br, 2H), 7.63 (br,
2H), 7.34 (br, 1H), 2.19 (br, 6H), 1.54 (br, 18H), 1.39 (br, 18H),
1.27 (s, 27H), 0.94 (br, 6H). 31P NMR (C6D6, 121 MHz) δ 55.6
(br). Anal. Calcd for C42H80BMnN3P3: C 64.20; H 10.26; N 5.35.
Found: C 63.84; H 10.10; N 5.22. IR (KBr/THF): ν(cm-1) 2048
(br).
[PhBPiPr3]Mn(1-Ph(isoindolate)) (8). A THF solution (10 mL)
of benzyl potassium (40.0 mg, 0.307 mmol) was added to a solution
of Hdbabh (59.4 mg, 0.307 mmol) chilled to -90 °C. The solution
was allowed to warm slowly to room temperature. After being
stirred for 24 h, the solution was rechilled to -90 °C and a THF
solution (10 mL) of [PhBPiPr3]MnI (203.9 mg, 0.307 mmol) was
added dropwise. After slowly warming to room temperature, the
orange solution was filtered through a Celite pad, concentrated under
reduced pressure to dryness, washed with petroleum ether, and
extracted with hot Et2O. Cooling the ether solution to -30 °C
afforded red-orange crystals (71.8 mg, 35% yield). 1H NMR (C6D6,
300 MHz) δ 11 (v. br), 8.2 (br). Anal. Calcd for C41H63BMnNP3:
C 67.59; H 8.72; N 1.92. Found: C 66.34; H 9.83; N 1.82.
[PhBPiPr3]Tl-MnBr(CO)4 (9). [PhBPiPr3]Tl (150.0 mg, 0.219
mmol) and MnBr(CO)5 (73.6 mg, 0.262 mmol) were mixed together
in 10 mL of benzene. The reaction mixture was heated at 50 °C
for 7 h. After cooling, the solution was concentrated under reduced
pressure to dryness, extracted with benzene, filtered through a glass
wool pipet, and concentrated to dryness. The yellow solids were
washed liberally with petroleum ether and extracted with benzene.
Acknowledgment. We gratefully acknowledge the NSF
(CHE-0132216)) and the NIH (GM 070757) for financial
support; the Beckman Institute (Caltech) for use of its
crystallographic facility and SQUID magnetometer; the
Materials and Process Simulation Center (Caltech, Goddard)
for use of its computational facility. We thank Dr. Theodore
A. Betley and Larry Henling for crystallographic assistance
and Dr. David M. Jenkins for assistance with SQUID and
EPR measurements.
Supporting Information Available: Crystallographic data and
CIFs for complexes 1a, 1b, 2-4, 6-10, and {(Hdbabh)MnI(µ-N-
dbabh)}2. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC060735Q
Inorganic Chemistry, Vol. 45, No. 21, 2006 8607